1. Field of the Invention
The present invention relates to an improvement in a liquid crystal display apparatus to be used to project an image on a screen or the like in an enlarged scale.
2. Description of the Related Art
Recently, a projector liquid crystal display apparatus, for example, is proposed as a liquid crystal display apparatus for displaying a television image and the like by using a liquid crystal display panel.
FIG. 1 shows a conventional projector liquid crystal display apparatus. Referring to FIG. 1, reference numeral 1 denotes a liquid crystal display panel. A TN (twisted nematic) type liquid crystal device is generally used as the display panel 1. The TN type liquid crystal device comprises a liquid crystal layer in which liquid crystal molecules are twisted; and polarizing plates 2a and 2b located at light incident side and output side, respectively. Reference numeral 3 denotes a light source arranged to oppose a light incident surface of the panel 1. The light source 3 includes a high-luminance light source lamp 4 such as a halogen lamp or xenon lamp; and a reflector 5 for reflecting radiated light from the lamp 4 toward the panel 1. The reflector 5 is a paraboloidal reflector having a parabolic shape for refecting the radiated light from the lamp 4 as parallel light parallel to an optical axis of reflector. Reference numeral 6 denotes a projection lens arranged to oppose a light output surface of the panel 1; and 7, a screen.
In this projector liquid crystal display apparatus, the radiated light from the light source 3 is incident on the panel 1. A display image on the panel 1 is enlarged and projected on the screen 7 by the lens 6. According to this projector liquid crystal display apparatus, a display image on the panel 1 having a small display screen can be viewed in an enlarged scale.
In the above conventional liquid crystal display apparatus, however, radiated light from the light source 3 is directly incident on the panel 1. For this reason, only about half of the radiated light from the light source 3 can be utilized in display on the panel 1. Therefore, since the luminance of a display image on the panel 1 is low, an image projected in an enlarged scale on the screen 7 becomes dark with poor contrast. This is because the panel 1 displays images by using only linearly polarized light transmitted through the incident-side polarizing plate 2a while the radiated light from the light source 3 is natural light including light components having various oscillation directions. More specifically, of the light from the light source 3, light having an oscillation direction which is the same as a direction of a transmission axis of the polarizing plate 2a is incident on the panel 1 through the polarizing plate 2a. However, light having a component in an oscillation direction perpendicular to the transmission axis of the polarizing plate 2a is absorbed by the polarizing plate 2a. Therefore, an amount of light actually incident on the panel 1 is reduced to about half that of the light from the light source 3.